1. Field of the Disclosure
The disclosure relates generally to antimicrobial resin compositions and methods for making such resins. More particularly, the disclosure is directed to methods of making antimicrobial resin compositions comprising antimicrobial metal salts and methods for forming such resins on substrates, such as medical devices.
2. Brief Description of Related Technology
Even brief exposure to surfaces contaminated with microbes can introduce bacterial, viral, fungal, or other undesirable infections to humans and other animals. Of particular concern is preventing or reducing microbial infection associated with the use of invasive medical devices such as catheters, intravenous fluid administration systems, and similar medical devices which require prolonged patient contact and thus present significant infection risks. Contamination may result from the patients' own flora or from one or more healthcare workers' hands during insertion and/or manipulation of the device, or from both the patient and healthcare worker. Medical devices coated with antimicrobial materials can reduce the transfer of such microbes to patients, thereby improving the safety and efficacy of these devices. Such antimicrobial coatings often include silver metal or silver salts, or other metals with demonstrable antimicrobial activity such as copper, gold, zinc, cerium, platinum, palladium, or tin.
Silver and salts thereof are commonly used in antimicrobial coatings because of their demonstrated broad spectrum antimicrobial activity against various bacteria, viruses, yeast, fungi, and protozoa. It is theorized that the observed antimicrobial activity is primarily due to the ability of silver ions to tightly bind nucleophilic functional groups containing sulfur, oxygen or nitrogen. Many nucleophilic functional groups such as thiols, carboxylates, phosphates, alcohols, amines, imidazoles, and indoles are prevalent in biomolecules. Upon binding of ionized silver to these various nucleophilic functional groups, it is believed that widespread disruption and inactivation of microbial biomolecules (and thus antimicrobial activity) occurs.
Silver and salts thereof have therefore been used as antimicrobial agents in a wide variety of applications; for example, they have been incorporated in the absorbent materials of wound care products such as dressings, gels, and bandages, and also in compositions for providing antimicrobial coatings on medical devices. Polymeric components frequently are added to such silver- or silver salt-containing compositions in order to facilitate manufacturing and/or deposition. One disadvantage of such antimicrobial compositions, however, is their characteristic poor adhesion to substrate surfaces. Strong adhesion to surfaces is frequently desirable to maintain continued release of the antimicrobial agent over a period of time and to avoid loss of the antimicrobial coating by routine contact with a patient or healthcare worker. Many polymer-containing metal or metal salt compositions also exhibit unsatisfactory antimicrobial efficacy profiles. Various factors can contribute to undesirable efficacy profiles, such as poorly dispersed or settled particles of the metal or metal salt, deformation of the coating during curing, or decomposition of the metal or metal salt during subsequent sterilization treatments. Poor dispersion of the metal or metal salt in the composition, for example, can result in heterogeneous release of the metal or metal salt, while a well-dispersed metal or metal salt generally elutes from the composition according to more homogeneous spatial and/or temporal release profiles. Another disadvantage of many polymer-containing metal or metal salt compositions is the heterogeneous crosslinked structure that can result, for example, from long polymer cure times and/or imprecise control of the polymer curing conditions. Long polymer cure times and/or imprecisely controlled polymer curing conditions, for example, can disadvantageously contribute to the formation of poorly dispersed or settled metals or metal salts, and thus can produce compositions having heterogeneous elution profiles.
A disadvantage of antimicrobial compositions comprising metals instead of metal salts is their characteristic color/opaqueness, which prevents a healthcare provider from being able to see through the medical device substrate. Silver coatings, for example, are generally brown in color. Thus, when silver coatings are applied to transparent surfaces, the coated surfaces typically have a brown color and significantly diminished transparency. In contrast to coatings comprising metallic silver, many coatings comprising silver salts are transparent or translucent, and/or lack a colored appearance. Thus, when silver salt coatings are applied to transparent surfaces, the coated surfaces typically have little color and are highly transparent.